I was sent Humble Audio’s Quad Operator along with its preset saver/storer/crossfader/expander/sidekick, Algo to test out, and at first sight, and the first thing that sticks out, is that it looks like a jungle of potentiometer knobs, which can be a scary endeavor. This plethora of knobs is sure to turn some off, and that’s fair enough—we are all entitled to our likes and dislikes—but that’s more of a shame than I have room to ruminate on here, because Humble Audio—which has nothing to be humble about concerning their first offering—has created a most excellent FM synth with a built in matrix mixer for Eurorack in their Quad Operator module. And so, while space is both available and absent, everything is well labeled, the layout is excellent, and it was never an issue to reach what I needed to—no machete or John Deere needed.

In terms of layout, on the left side of the module, Quad Operator sports four distinct interconnected variable waveshape operators, each having a potentiometer to control RATE, SHAPE, and GAIN, and each sporting a CV input to be modulated by something other than your fingers. It can be easy for those with larger digits to get tangled in the plethora of knobs no matter how organized they are, but I personally had no problems with this. Each operator has the ability to have the pitch run wild and free or be on lockdown. While I was testing the Quad Operator—beginning in late March—I myself was in lockdown mode in Seattle due to the Corona virus.

During the testing, I was also in the midst of prototyping this issue’s DIY project, the Catwalk Ribbon, and it was interesting to run it into the RATE of a channel to hear the difference between the LOCK vs. FREE [coming soon to Netflix!] modes. As the manual states, when in LOCK mode “each operator adheres to a strict integer frequency ratio relationship [1/11th to 11 multiplier relative to master coarse/fine in integer steps] to the master coarse and fine tuning,” and swiping the ribbon controller resulted in a quantized sound that spanned several octaves. LOCK is what you’ll want to be on if you want to utilize Quad Operator in it’s best usages as it produces typical [and atypical] FM sounds. Each operator also has a DETUNE knob so you can pitch sonic battles between operators and listen to their frequencies bump up against one another and duke it out. Also in the upper left you will find the strange, yet pleasing conical knobs, shaped like Moroccan tagines, for global COARSE and FINE pitch control. There is a switch to go from VCO to LFO as well, and while I mainly used Quad as a VCO, you can really get super nutty with it in LFO mode. I found it great for making bug/nature sounds on its own without modulating a filter or VCA or anything. It’s a very interesting alternative to your standard sine/saw/square wave LFO, and I’m not sure I’ve ever had an LFO that was so...rebellious.

In the middle of the module towards the bottom, is a global input with attenuator for AR [audio rate] FM over all operators, with each operator having a dedicated attenuator to dial this in, and a GAIN CV in to modulate that, good for a tremolo type of effect.

The right side of the module is the matrix mixer, where each operator has attenuators for the other three operators as well as its own, to dial in the various amounts of interaction. At the bottom of this is the row of AR attenuators, and below that, at the very bottom of the module is where you’ll find the outputs.

Starting off with a simple patch by outputting one channel into your mixer and trying out that channel’s available parameters can bring about enough sonic possibilities to keep you experimenting for quite a while, and when you add three more channels/outputs with the same possibilities, and the ability to interconnect them all, you will undoubtedly—as I did—get lost in a sonic maelstrom. Manipulating the functions on one channel to hear the interaction, the changes, the overall domino effect it can have on the other operators is revelatory. In the thick of it I got sounds ranging from falling backwards into a digital abyss to the annoying sound of sucking on a straw to extract the last sacred drop of Mt. Dew Code Red or Cookie Dough Blizzard [pick your poison]. I found myself losing track of time, and—while not necessarily making music per se—getting lost in sound, experimenting with and pondering the inter-relationships between waveshapes, and musing on how one small change can affect so many different things, a thought process that seemed very much in line with the global situation at the time.

The Quad Operator is an extremely fun sound machine and versatile, as it can be used as just 4 VCOs/LFOs or as complex as you’d like to get. It’s an FM playground of dreams, and seems like the kind of thing that came to fruition in one of those “Wouldn’t it be crazy if…” brainstorm sessions. There is, however, a saturation point, as with anything with so many options. It’s kind of like when you keep adding colors to something and eventually it just turns brown. What I’m trying to say is that if you don’t show some restraint, you won’t be able to see the potentiometer forest from the potentiometrees . The Quad Operator tracks well at 1V/octave, though again, if you don’t show restraint you’re just going to get different pitches of brown.

Moving on to the Algo, the Quad Operator’s crossfading preset manager—which stores up to three presets—this also lets you return to your live setting, and enables you crossfade between any two of them, including the live setting, or just stay on one. It even saves the stored presets after power down and is dead simple to use. I’d say that if you get the Quad Operator you should definitely do yourself a favor and get Algo as well, as you’ll be missing out if you don’t.

There are really no drawbacks with the Quad Operator/Algo, so long as you’re cool with the large plethora of small knobs and have the space to rack it. Honestly, this is one module that would also work really well cased on its own, and I’m a little surprised there isn’t that option available. A lot of the time I spent with it I wasn’t using anything else, just creation from within, and seeing as how it was during the beginnings of the lockdown, it was also a time when I thought a lot about minimalism. How much is too much? Truly, what are necessities? It was easy to talk myself into thinking I was being a minimalist synthesist when the one module I was testing had so much to offer. It made me rethink what I thought of minimalism to begin with. And yet I think this is one module there is a lot to learn from. It’s obvious how much exploration is possible, but I really felt a sort of Zen connection with it, something I’ve never felt with another module before. Maybe it’s the layout, maybe it’s the interconnectivity, maybe I just like the idea of humbleness.

I will say this one thing, that it would be amazing to be able to CV the amount of each operator going into the others, which would of course result in another 16 CV ins—a huge real estate development—which, if I can have my own, “Wouldn’t it be crazy if…” would make one enormous, yet crazy cool FM synth. If FM is your game, Quad Operator is your game on.

30HP +12V 140mA -12V 13mA

W/Algo [4HP]+12V 145mA -12V 13mA

Price: $500, Algo Expander $85

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